Hammock With Adjustable Curvature

ABSTRACT

This invention relates to a hammock for use by people for leisure or sleeping. It provides adjustable features that allow the users longitudinal curvature to be flat, or curved upward, or curved downward, or both with the head and feet raised to different and opposing levels with respect to the flat configuration. This adjustable longitudinal curvature control enhances user comfort during leisure and enhances the ability to sleep in this hammock.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

This invention relates to a hammock for use by people who wish to lay down in a prone and essentially flat position for leisure or sleeping.

Hammocks provide a user with a bed like surface for body support that can be connected between upright structures (e.g. trees, posts, fixed walls, etc.) on which a person may lie suspended above the ground. Traditional hammocks are typically constructed of a sheet of material, often flexible fabric (e.g. canvas, nylon fabric, netting, ropes, etc.) gathered at the ends and suspended from upright structures by ropes, straps or like means.

One drawback of traditional hammocks is known as hammock sag, whereby the middle of the hammock sags below the ends creating a longitudinally curved supporting surface. Such a curve along the users' longitudinal surface may be uncomfortable for the occupant as it does not follow the natural profile that the person's body will take when lying down on a typical flat bed, and the upward curvature often bothers a users knees because the users legs are straight and do not get adequate support from the longitudinal curved hammock surface in the middle so the knees tend to hyperextend and become stressed and uncomfortable. Furthermore, traditional hammocks are unstable and prone to tipping, and are not user adjustable adequately, other than tensioning the hammock, for slight control of the users' body longitudinal curvature.

PRIOR ART IN THIS AREA INCLUDES

There have been a number of attempts to provide so-called self-leveling hammocks in an effort to reduce the aforementioned problems. For example, Brazilian hammocks provide an extra wide sleeping surface so that a person may lie diagonally. Such hammocks require extra material and an occupant must be careful not to move into a non-diagonal position. U.S. Pat. No. 6,701,549, U.S. Pat. No. 645,805, U.S. Pat. No. 249,403, U.S. Pat. No. 202,814, U.S. 2002/0042951 and 30 U.S. 2004/0006820 all describe various ways of compensating for hammock sag.

U.S. Pat. No. 7,020,915 also uses a suspension type hammock design, but it attempts to preplan a manufactured in location for knee and lumbar support for a user that are not adjustable and therefore cannot meet the geometry requirements of a 5th percentile to 95th percentile user. Further it incorporates closed ends with storage areas that add weight, cost, and added installed length requirements for the design. Further the closed end designs are not ideal for use in hot and humid environments due to the closed ends blocking of cooling wind and breezes.

None of these prior art designs have been wholly successful at providing a comfortable, stable, substantially flat sleeping surface in a portable, easy to set-up hammock, and adjustments are limited, cumbersome, complex or nonexistent.

This invention overcomes all of these aforementioned limitations in the prior art. It allows a user to adjust the hammock for a flat prone sleeping position based on their own body geometry and weight and installation location variations. This invention also allows adjustments to provide a longitudinal body curvature upward, downward, or both varying from head to foot. This adjustability in longitudinal body curvature combined with the natural compliance of a suspension type hammock using slightly compliant materials like nylon webbing for the main tensile suspension member and nylon fabric (or similar high strength sheet materials) for the support surface provides ideal and adjustable support for lumbar and knees as well as head and feet position with respect to body position. This invention also has an open geometry with no extra flaps or storage areas to block a breeze allowing good open-air exposure suitable for added comfort in hot and humid environments.

This invention also has two attachment variations, first a long set of mounting straps built into the hammock for general purpose attachment using these longitudinal oriented straps between vertical supports like trees when the longitudinal length of the installation is not constrained in dimension, and second a short set of loops built in allowing connection to rigid mounting points oriented laterally directly at the end of the hammock when a fixed site installation is desired and the longitudinal dimension is limited. This invention is also a practical and efficient minimalist design that is light weight, and lowers the cost of manufacture making it more suitable to campers and backpackers and other larger market segments, and due to its light weight, simplicity and potential for lower cost.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a hammock for use by people for leisure or sleeping. It provides adjustable features that allow the users longitudinal curvature to be adjusted to be more flat, or curved upward, or curved downward, or both with the head and feet raised to different and opposing levels with respect to the flat configuration. This adjustable longitudinal curvature control enhances user comfort during leisure and enhances the ability to sleep in this hammock.

This invention carries the horizontal tensile loads due to the weight of the user in the hammock by using a suspension means composed of two flexible tensile suspension member on either side of the hammock, like a suspension bridges main suspension cable, with the user supporting fabric or sheet surface blank draped between and below the suspension member. The fabric or sheet user support surface, also called a blank or bed surface, uses smoothly curved side profiles that are symmetrical side to side and are narrower in the center of the hammock and wider at each end.

The profile of the curved sides may use a partial section of a parabola, catenary curve, circle, ellipse, hyperbola or similar suitable transcendental function, where said fabric blank sides are supported in tension laterally from side to side only and drape down laterally along the full length of each side. The fabric blank can use a continuous attachment loop of excess side material to wrap around the suspension member, or a sewn seam or similar means of attaching it to the main suspension members routed longitudinally on either side.

Adjustment of a user's longitudinal curvature is possible for a given range of load conditions during manufacture by adjusting the ratio of the hammock support fabric width in the center of the hammock to the width at each end. Adjustment of the hammock by a user to adjust the users longitudinal curvature is also possible by an end user after the time of manufacture and during set-up prior to use with two approaches, first by adjusting the tension in the hammock between the supporting attachment points, and second by providing for a user adjustment of the side to side dimension between the two high-tension flexible suspension load bearing members (nylon webbing), by using adjustable width cross brace or cross brace or lateral support members with one at each end of the hammock.

The adjustable width cross brace or lateral support member may be made using a discrete number of tubes attached end-to-end, or a telescoping pole with clamps to hold a given dimension, or telescoping tubes with pins or attached spring loaded pins to allow cross brace or lateral support member length adjustment. However, for the lowest weight and cost and reliability the preferred embodiment of the adjustable width cross brace or lateral support member is a discrete number of tube sections that can be user adjusted to allow control of the members length, and therefore the width when installed at the hammock ends.

In the preferred embodiment this adjustable width cross brace or lateral support member consists of a multitude of tubes connected together with connecting cylinders, such that the user can use fewer or more of said cylinders to achieve control over the extended length of the cross brace or lateral support member (corresponding to the lateral width of one end of the hammock between the suspension members) and thereby the width of the hammock on each end. By increasing the separation between each sides flexible suspension load bearing members with the adjustable width cross brace or lateral support members, a user can control how much to raise the respective end area of the hammock with respect to the nominal flat configuration, and conversely by bringing the flexible suspension load bearing members closer together using the adjustable width cross brace or lateral support members, a user can control how much to lower the respective end area of the hammock with respect to the nominal flat configuration.

At both ends of each adjustable width cross brace or lateral support member is a retaining feature, designed to allow one end loop and strap segment of the high-tension flexible suspension load bearing member (webbing) to be routed through a hole or slot and also attach to or constrain the cross brace or lateral support member end, thus retaining the webbing at a controlled width at the end of the hammock based on the users control of the cross brace or lateral support member length.

Attachment points for the flexible suspension load bearing members on the end of the hammock can be done either using short loops, formed integrally with the end straps, for applications where the longitudinal dimension allowed by installation site constraints is an issue, or full-length straps terminating in loops where ample longitudinal length is available and lower overall weight is a priority. These are two alternate configurations, or they can be merged into a single strap design with both short loops and long loops on the same strap, as a variation of this invention. Further, the long straps can be tied with a knot near the hammocks end to also implement the short strap variation. These two alternatives are shown as variations in this invention disclosure, but it is to be understood that all variations of short and long straps with looped ends or other high-tension flexible suspension load bearing members end attachment provisions are incorporated in this invention.

In addition to suspending the hammock from a typical vertical support like a pair of trees or poles, the shorter loop configuration is also suitable for installations that can provide four rigid supports for all four attachment points, and preferably also two or more lateral distances between support points in place of the cross brace lateral support members, so that applications to marine, submarine and specialty automotive and similar applications can be accomplished in a compact and comfortable fashion.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A shows a calculated parabolic curve with the longitudinal length and curve inset adjusted to the dimensions determined for one specific embodiment of this invention. This parabolic curve corresponds to the profile cut into each side of the hammock blank to make it wider at the ends and narrow in the center of the hammock blank.

FIG. 1B shows a plan view of a sheet of flexible fabric, called a blank, using a parabolic curve for the profile of the curve cut into the sides of the blank. The longitudinal length and minimum and maximum width of the side to side dimension can be varied to suite a class of user or specific application design criteria. Here a 90 inch length, 29 inch center width, and 57 inch end length for each end is used, with the parabolic side curve inset maximum of 14 inches on each side, the typical nominal design dimensions of our preferred embodiment.

FIG. 1C shows an example side curve for this invention, illustrating a circular curve side profile and the first and second derivative of the circular curve, emphasizing the desirable qualities of a smooth curve with a single dY=0 point emphasizing a single tangent point aligned with the hammocks central longitudinal axis, and a unipolar d²Y emphasizing a smoothly changing rate of change of slope, characteristics that are important for reducing stress points on a suspension member attached to a connecting member, in this invention the draped fabric bed support.

FIG. 1D shows an example side curve for this invention, illustrating a parabolic curve side profile and the first and second derivative of the parabolic curve, emphasizing the desirable qualities of a smooth curve with a single dY=0 point emphasizing a single tangent point aligned with the hammocks central longitudinal axis, and a unipolar d²Y emphasizing a consistent rate of change of slope, characteristics that are important for reducing stress points on a suspension member attached to a connecting member, in this invention the draped fabric bed support.

FIG. 1E shows an the side curve of prior art in U.S. Pat. No. 7,020,915, illustrating a non-uniform scalloped side profile and the first and second derivative of that non-uniform curve, emphasizing the undesirable qualities of an unsmooth curve with multiple dY=0 points, emphasizing multiple tangent points aligned with the hammocks central longitudinal axis, thereby increasing the 3 dimensional stress concentrations at the intersections, and a bipolar d²Y emphasizing a non-consistent rate of change of slope, characteristics that are detrimental for reducing stress points on a suspension member attached to a connecting member, or the non-uniform draped fabric sheet or blank used as the bed support.

FIG. 2 shows five views of different hammock side profiles with a common heading and comparison points allowing direct comparisons of important differences in the side profile curves of the hammocks, directly illustrating how views FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D differ from the prior art shown in FIG. 2E. FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D all have smooth, continuous curves that are symmetrical about the Y axis, where the Y axis is the hammock side profile inset cut into one side of the hammock sides and the Y axis is located at the minimum point of Y as a function of X, and these side profile curves all have Y values monotonically increasing for positive X values, (and by symmetry also in the opposite direction for negative X values) and do not contain any straight sections, and do not have multiple dY=0 points along the curved side profiles, and have a unipolar d²Y. By contrast the prior art of U.S. Pat. No. 7,020,915 summarized in FIG. 2E differs in the hammock side profile curve in each of these metrics emphasizing the differences.

FIG. 3A shows a plan view of the flexible fabric blank after attaching the continuous tensile suspension member, typically 1 inch wide nylon webbing, along the two curved side surfaces, typically using a loop of excess side material around the suspension member or by machine sewing methods of the sheet fabric blank to the suspension member, and also incorporating short attachment loops at the ends of the suspension member (webbing).

FIG. 3B shows a plan view of the flexible fabric blank after attaching the continuous tensile suspension member, typically 1 inch wide nylon webbing, along the two curved side surfaces, and incorporating long attachment webbing lengths typically using a loop of excess side material around the suspension member or by machine sewing methods of the sheet fabric blank to the suspension member, and terminating in loops at the ends of the suspension member (webbing), a general-purpose configuration of this invention.

FIG. 4 shows a line drawing derived from an actual photograph for realism, showing the shape of the hammock when unloaded, but attached between two supporting trees for example. The draping of the fabric support blank between the high-tension flexible suspension load bearing members on either side can be seen varying from a large amount of drape at each end and progressively less towards the center of the hammock.

FIG. 5 shows a line drawing, derived from a photograph with a 190 pound user in the hammock, showing the substantially flat laying down position of a user of the hammock of this invention.

FIG. 6 shows multiple options for the adjustable width cross brace or lateral support members using the preferred embodiment approach of multiple tube sections interconnected and with special end caps to retain the straps of the high-tension flexible suspension load bearing members (webbing attached along each side of the hammock).

FIG. 6A shows a simple two segment configuration for example, shown in an exploded view to illustrate the two tube sections with individual slip-on end caps with a hole or slot through them to capture and constrain the high-tension flexible suspension load bearing member (rope, cable or webbing) when it is inserted into the hole, and with a slip on tube coupler at each end of the end caps oriented toward the central tube side, and one slip on center connecting tube coupler between the two tubes.

FIG. 6B shows this assembly in the final assembled configuration after a user has slipped all the parts together.

FIG. 6C shows the same assembly as FIG. 6B but now in a side view.

FIG. 6D shows a different assembly variation using now four shorter tube segments, connected with two end caps and three tube couplers connecting the inner tube sections together. More tube sections gives more user control of the overall length variations of the adjustable width cross brace or lateral support member.

FIG. 6E shows a similar assembly as FIG. 6D but now with the two inner most tubes of a larger diameter, with one center coupler for the larger tubes, and two transition tube couplers to couple the larger center tubes to the smaller diameter outer tubes. This configuration has a larger diameter tube at the center of the assembly increasing its buckling resistance when in compression during use thereby increasing the hammocks load carrying capability. This configuration also has the advantage of allowing packing the two outer tubes inside the two inner tubes for transport compactness.

FIG. 6F shows this preferred embodiment of the adjustable width cross brace or lateral support member using two tube diameters in a fully assembled isometric view, with the nominal number of sections (4). One of these assemblies would be used at each end of the hammock.

FIG. 6G shows the same assembly as FIG. 6F but now in a side view for clarity and comparison.

FIG. 6H shows a user reconfiguration of the nominal number of tube segments, now using three tube segments to provide a shorter overall length to allow adjustment of the hammocks end width constraint to lower that end of the hammock where it is installed.

FIG. 6I shows a reconfiguration of the nominal number of tube segments, now using five tube segments to provide a longer overall length to allow adjustment of the hammocks end width constraint to raise that end of the hammock where it is installed.

FIG. 7 shows the hammock adjusted for raising the users head (with a longer cross brace or lateral support member configuration), and lowering the users feet (with a shorter cross brace or lateral support member configuration) as an example of the users control of users bodies longitudinal curvature enabled by this invention.

FIG. 8 shows four different positions the user can adjust for by using overall tension of the hammock end straps and the assembled length of the adjustable width cross brace or lateral support members, including (A) upward center of curvature, (B) substantially flat configuration, (C) downward center of curvature, and (D) with the head up and feet down configuration. In all cases the users center of mass is located below the high-tension flexible suspension load bearing members (webbing straps) making this hammock stable from rolling or falling out laterally.

FIG. 9 shows the completed hammock with a user enjoying this invention and illustrating the compliance of the materials around the users complex geometry including support for lumbar and similar body curve sections, enhancing user comfort without any specific user curvature assumptions during the point of manufacture.

FIG. 10 shows a line drawing of a plan view of a complete hammock kit assembly showing and detailing the individual parts in a typical configuration suitable for use between two trees or other vertical support members.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

This improved hammock design utilizes a dual high-tension suspension element type design approach. This approach is analogous to a roadway suspension bridge that uses two top cables on either side of the road supported below, with high-tension top cable strength and support capability, and a plurality of smaller cables draped down to support the road surface.

However, due to this inventions use of slightly compliant materials for the fabric blank support sheet that are common for making hammocks, like nylon webbing for high tension suspension cable application and nylon or polyester (for instance) sheet fabrics for flat fabric blank material, compliance of the supporting surface is accomplished as the load is applied by a users body when laying in the hammock. Therefore, in order to end up with a flat, or nearly flat user support surface once loaded, the sheet fabric width is necked down in the center using a smooth continuous curve toward the center of the hammock, and it widens as it approaches each end.

The shape of the side profile of the blank is relevant to the flatness and amount of compliance and final longitudinal curvature of the hammock, and the resulting support surface of the hammock upon which the user will lay. Since the support for the fabric blank is purely vertical applied by the tension of the sheet fabric blank vertically draped between the two high-tension flexible suspension load bearing members on either side, this application is similar to the suspension bridge design.

It is generally understood that a suspension bridge high tension support cable takes a shape of a catenary curve or possibly a parabolic curve when under load. These two shapes are extremely close to each other, to the point that it is difficult to visually differentiate the two. Further these shapes are known to be optimal or nearly optimal for supporting a load with an essentially equal and homogeneous load along the length of the cable. Therefore, these two curves are ideal candidate for the shape of the side profile of the hammock sheet fabric blank.

FIG. 1A shows a parabolic curve with corresponding X and Y coordinates for making a simple parabolic curve for the sides of the hammock. This shape is the preferred embodiment since it reduces stress on the suspension member and the attachment to and stresses in the sheet fabric blank. In this example, the length of the hammock is assumed to be 90 inches, and these coordinates are considered to be along the X axis. For this example of a parabolic side profile, the Y axis is a scaler coefficient times the square of the distance from the center of the hammock longitudinally. The Y axis corresponds to the amount of inset cut into each side of the hammock in the lateral direction (side to side) as a function of the X coordinate longitudinally. For symmetry the Y coordinate system origin is placed at the longitudinal location with the minimum width near the center of the sheet fabric, for purposes of discussion. In this case, using symmetry longitudinally about the centerline and laterally about the centerline, the hourglass type shape shown in FIG. 1B results. Item 100 is the flexible fabric blank that composes the users body support surface, typically made of high strength fabric like nylon, polyester, or similar fabrics. The parabolic curve scaler coefficient is calculated by considering the width of the ends and the width of the center desired for the user and application based on users general geometry and weight assumptions. This invention also incorporates alternative variations (ramifications) where the head end of the hammock and the feet end of the hammock are different widths, and the curved (parabolic for example) side profile is not symmetric end to end.

The shape of the ends of the blank are not critical to the function of this hammock, and the simplest form of a straight line is used here for example. Other variations in the head and feet end shape (flat, curved, scalloped, etc.) are also obviously possible and are incorporated into the invention described herein.

While a parabola side shape is used in the example of FIG. 1 shown, it is also possible to use other curves and obtain other support characteristics with slight variations in terms of flatness or curvature.

A comparison of different curves is shown in FIG. 2, highlighting the scope of this patent as applicable to all curves that are smooth, continuous, and have a central or non-central axis of symmetry longitudinally with respect to the two hammock ends, are symmetrical about the hammocks longitudinal centerline axis, and have a single Y(X)=0 point and a unipolar d²Y(X). Details of these qualities can be seen in FIG. 1C for a circular curved side, and 1D for a parabolic curved side. This distinction characterizes the properties that are relevant for a high-tension flexible lad bearing member suspension support system suitable for allowing the users lying prone position to be flat, and using a compliant material like nylon webbing and nylon sheet fabric, in order to distribute the load as evenly as possible and avoid load and stress concentrations, and to make the hammock light weight and essentially flat for users ranging from 5th to 95th percentile for height, weight, and body geometry and density. Further, this mathematical definition highlights a key difference of this invention versus the prior art of U.S. Pat. No. 7,020,915. This is illustrated in FIG. 1E, highlighting that is prior art is not symmetrical longitudinally (e.g Y(X) is not equal to Y(−X) about any Y origin along X, it has multiple points where dY(X)=0, and is bipolar for d²Y(X), all qualities that will cause stress concentrations in the hammocks fabric and pressure points for users that do not match up perfectly with the designed-in geometry of the side curve and resulting bed surface for knee and lumbar support of 5th to 95th percentile users. Thus this prior art will not provide a flat bed resting surface for the majority of users between the 5th and 95th percentile for size and weight, and it is not adjustable.

For this invention, whatever smooth circular curve is selected for the hammock side profile based on the application (general user weight, height, density distribution, etc.) the desired curve is then formed into the actual hammock by cutting out the blank to the desired hourglass like shape (100), then looping excess side material around the suspension member or machine sewing, bonding, gluing or otherwise fastening the sheet fabric blank to two side mounted high-tension flexible suspension load bearing members (101), typically a continuous length of nylon webbing or similar material. Typically, this is done by looping excess side material around the suspension member then machine sewing the sheet fabric to the webbing continuously along the side profile, and providing for an extra length of webbing at each end for either a short loop for attachment, or a long strap and then a loop for attachment, or a combination of both of these loop options on the same strap. The loop at the end of these straps is typically connected to a carabiner and then to another long extension strap to attach it to a vertical support tree or post or similar support point of the users selection. These two main construction options are shown in FIGS. 3A and 3B respectively. In these Figures item 100 is the flexible fabric sheet blank, item 101 is the high-tension webbing attached to each of the hammock side edges, item 102 is the short webbing loop attachment points constructed of the same side webbing and looped back upon itself and attached or stitched at the loops intersection to reinforce them and form a high-tension support loop, and item 103 are the long straps leading to the end loop attachment points 104. This approach has the construction advantages of simplicity, and high strength and low weight.

In addition, the two ends of the hammock sheet fabric blank may be flat or any shape desired, and hemmed only, or reinforced in a similar way to the sides by using additional webbing and stitching or similar means, although the ends are not a high-tension load carrying seam under normal use and it is less important reinforce them from a mechanical strength properties perspective. This hem or webbing reinforcement is shown as item 116.

FIG. 4 shows a perspective view of the completed hammock under typical installation tension for clarity, with adjustable width cross brace or lateral support members (105) located at each end of the hammock and each constraining the width of the high-tension flexible suspension load bearing members (ropes, cables or webbing) (103) at their respective ends. Further it shows the longer webbing straps (103) and terminating loops (104) suitable for attachment to a carabiner.

FIG. 5 shows a typical installation of this invention in this type user scenario, configured for a flat support position. It is important to note in this image that the users center of mass and all of his body length is located below the suspension members on both sides, making this design stable and not prone to tipping laterally.

For a typical user that wants to adjust the hammock flatness, this invention requires an adjustable width cross brace or lateral support member at each end of the hammock, such that the high-tension suspension webbing member loops or straps are constrained to remain at a preset dimension, but also a user adjustable dimension. In the simplest form, with minimal adjustment, this can be done using two cylinders (106) like the ones shown in FIG. 6A in exploded view, that are designed for high compression loads, supporting two slip-fit end caps (107), one slipped onto each end, each end cap with a hole or slot to constrain the webbing straps (103) separation when under load, one at each end of the tube assembly, separated by the correct dimension as set by the user for the user preference and application. Further FIG. 6A shows a slip fit center tube to tube coupler (108) used to connect the tubes together using a slip fit user assembly method.

FIG. 6B shows this item fully assembled with the slip fit end caps and one slip fit center coupler. This adjustable width cross brace or lateral support members tubes can be made from a thin wall aluminum, steel, or composite material for the tube sections, and machined or injection molded end caps with a hole or guide slot for constraining the webbing, plus a single central tube to tube coupler also machined from aluminum or similar high strength material. The end caps each have one hole or slot sized so that the nylon webbing high tension suspension load bearing member (webbing) straps will pass through them. A further constraint for the construction of this cross brace or lateral support member is that it must not buckle when subjected to the installation strap geometry and loads. This is a straightforward calculation for column buckling, known by mechanical engineers, with two simply supported ends and is published in most college level mechanical engineering books. Typically, an aluminum tube of 0.75″ diameter and a wall thickness of at least 0.035″ is adequate for the aluminum tubing material up to 4 feet in total length, which is then cut to shorter lengths depending on the number of tube sections desired. The nominal tube length for the preferred embodiment of this invention is 36 inches, but slightly more or less may be suitable depending on the blank dimensions.

In order to make the hammock smaller when packaged and transported it is desirable to make this adjustable width cross brace or lateral support member as compact, lightweight, and low cost as possible. Therefore, as a preferred embodiment, shown in FIG. 6E, a high tensile material (like 6061-T6 aluminum tubing 1.0″ outer diameter and 0.035 inch wall thickness (or equivalent strength steel, or composite fiberglass or carbon fiber) is used for the inner tube sections (2 each) (109), and two more tubes of a lesser diameter (110) (typically 0.75″ outer diameter and 0.035″ wall thickness) are used for the two outer tubes. These two outer tubes similarly terminate with an end cap (111) with a hole or slot that can pass the nylon webbing high tension suspension strap (103) and looped end (104). Each end cap is added on the ends of tubes (110) with a slip fit and is machined from 6061-T6 aluminum or injection molded nylon or of similar high strength materials, and is dimensioned so it allows a user slip fit so it can be moved between tube segments depending on the number of segments to be used, and so that it will nest inside the end of the tube snugly and apply an axial compression load precisely to the tubes ends along the center axis of the tube. A center large coupler (112) is used to connect the two larger diameter tubes together with a slip fit, and a transition coupler from the larger tube inner diameter to the smaller tubes inner diameter (113) is also used to allow user assembly of the desired configuration and number of tube segments. This configuration is shown in FIG. 6E as an exploded perspective view and in FIG. 6F in assembled perspective view and FIG. 6G in assembled side view. This is the preferred embodiment for this invention, and the nominal number of tubes for further discussion.

The advantage of more segments is that one end of the hammock can use a different number of these cross brace or lateral support members to change the distance of separation of the high-tension suspension members, typically webbing, and thereby the height of the user support surface, or blank. By a user removing the number of cross brace or lateral support member tubes so the overall length is shorter than the nominal flat configuration, as user can control the resulting effect of lowering that end of the hammock support surface. An example of a reconfigured shorter cross brace or lateral support member, as configured by a user based on preference, is shown in FIG. 6H.

Conversely, adding additional cross brace or lateral support member tube segments will have the effect of increasing that end of the hammocks cross brace or lateral support member width, thereby raising that end of the hammock support surface fabric blank (100). An example of a longer cross brace or lateral support member is shown in FIG. 6I. This adjustability can be easily understood by considering the length of sheet fabric blank at the end of the hammock, and how far the sheet fabric blank will drape down under the cross brace or lateral support member in no load conditions. Typically a user may have extra tube sections of both the larger diameter and smaller diameter tubing, and additional couplers, to allow reconfiguration and adjustment to their liking.

When designing the cross brace or lateral support member tubing segments and couplers and end caps, buckling calculations must be performed on the worst-case configuration possible to assure buckling failure does not occur to the adjustable width cross brace or lateral support member when loaded by a user occupying the hammock. Limiting the minimum length of each extension segment is one way to be sure the permutations of separator lengths are calculatable, and buckling loads can be calculated, and a safe design with a margin of safety that will not buckle in all cases can be assured.

There is no minimum limit on the shortest cross brace or lateral support member length, and even a single unit may be used or none at all. The maximum number of tube segments and the corresponding cross brace or lateral support member width can be limited by providing user directions given to the users in an instruction booklet, and placing warnings on the tubes, and additionally by providing a product with a limited number of tube segments. From a practical perspective the maximum cross brace or lateral support member width is also limited by the end width of the flexible fabric blank as a maximum width.

FIG. 7 illustrates a side view of the hammock derived from a photograph and carrying a user of 190 pounds of weight, when properly adjusted for the user to have the head end higher and the feet end lower than the nominal flat configuration. The adjustments are the width of the cross brace or lateral support members at each end of the sheet fabric blank support surface, and the flat configuration is normally a nominal number of lateral support sections, like four tube members. In the example shown in FIG. 7, the head end would be raised by using 5 tube sections in that head end cross brace or lateral support member, and the feet end of the hammock would be lowered by using 3 tube sections in that feet end cross brace or lateral support member.

FIG. 8 illustrates a side by side comparison example of the longitudinal curvatures possible and controllable by a user with this head end and foot end cross brace or lateral support member length adjustment technique, ranging from 8A with an upward center of curvature, 8B with a substantially flat prone position, and 8C with a downward center of curvature (arched back), and finally 8D with the head up and the feet down for example.

FIG. 8A shows a configuration with more than the nominal number of tubes (5 each tube segments) for both the head end and the feet end of the hammock, producing a head up and feet up lying position for the user. FIG. 8B shows a nominal configuration (4 each of tube segments) resulting in a substantially flat lying position. FIG. 8C shows a configuration with fewer than nominal number of tube sections (3 each tube sections per lateral support tube), thus lowering the head end and feet end of the hammock support surface. Finally FIG. 8D shows the head end raised using more than nominal number of tube sections (5 each) and it shows the feet end lowered using fewer than nominal number of tube sections (3 each) lowering the feet below the flat configuration.

This user adjustment capability of their laying position longitudinal curvature in the vertical plane by modifying the number of tubes installed allows a user to control their specific preference for their bodies longitudinal curvature in the vertical plane, thus allowing them to obtain the most comfortable position for relaxing or sleeping depending upon their comfort preferences.

Since there is a substantial interaction of the designed shape of the hammock fabric blank side curve, the ratio of the sheet fabric blanks center minimum width to the sheet fabric ends maximum width, and the mounting geometry and tension and user geometry and density, and the number of tube sections and their length, an empirical approach was used to determine the most general and adjustable case and the curve and width parameters were determined. The images shown in this invention disclosure use a minimum blank width of 29 inches in the center of the hammock, and a maximum width at each end of 57 inches, and use a parabolic side profile with 14 inch maximum side curve inset as disclosed in FIG. 1. The nominal tube length is 36 inches, and the tube segments are 9 inches long each, and the tube diameters are 1 inch for the two center tube segments and 0.75 inch for the two outer tube segments, both with a wall thickness of 35 thousandths of an inch or greater.

One result of this construction is the shape of the hammock is unusual when unloaded. FIG. 4 shows an actual hammock prototype photograph converted into a line drawing illustrating how the bottom of the hammock support surface or blank has the center of longitudinal curvature oriented downward when unloaded. This same hammock is shown again with the complex body geometry and density distribution for an experimental user in a photograph converted to line drawing with a perspective view in FIG. 9, showing the user in a substantially flat prone body stance for maximum comfort, illustrating the validity of the invention design approach put forward herein.

FIG. 10 shows an overall plan view of the individual pieces of this hammock invention for context. It highlights the main parts of a complete hammock kit suitable for use by a user for camping or similar outdoor applications where the hammock is to be affixed between two trees. The main parts of this invention are (100) the flexible fabric blank, (101) the high-tension flexible suspension load bearing member (webbing), (103) each sides attachment strap (webbing) that terminates in a loop (104), where each strap (103) is routed through the end cap retaining hole or slot in the adjustable width cross brace or lateral support member (105), and where each loop (104) is coupled at each end to a commercially available carabiner (114) then to a readily available commercial tree attachment strap with end loop adjustment and fastening capability using a high-tension capable buckle or similar conventional means (115). 

What is claimed:
 1. A hammock comprising: a bed formed from a blank of strong flexible fabric, the blank defined by opposed ends and opposed sides, the ends and sides of the sheet of fabric coinciding with opposed ends and opposed side edges of the hammock respectively, each side of the sheet of fabric having a smoothly curved shape that is narrower in the middle between the ends, and wider at each end, and each side having a curve that can be measured as an inset dimension along an axis Y, called the lateral axis, that is parallel to the two parallel ends, and an axis X, called the longitudinal axis, that goes from the corner of one end and side of the blank to the corner of the other end and that same side of the blank, so that the side curve can be described by a function Y(X), and where the first derivative of Y(X), called dY(X) has a single point where it is zero, and where the second derivative of Y(X), called d²Y(X) is unipolar (either always positive or always negative for all X along the side curve), where the polarity of d²Y(X) is determined by the choice of direction of Y as toward or away from the hammocks other side), and where d²Y(X) is not bipolar (both positive and negative values for all X along the longitudinal axis).
 2. The hammock of claim 1, wherein the connecting means comprises a loop of material formed by an excess length of the side edges.
 3. The hammock of claim 2, wherein the connecting means on each side of the hammock is connected to the suspending means on each side of the hammock by routing one suspending means on each side of the hammock through the loop of material along each side of the hammock, and the connecting means may or may not be attached to the suspending means.
 4. The hammock of claim 3, wherein the suspending means comprises a high-tension flexible suspension load bearing member like a strap, webbing, rope or cable, with at least one high tension loop in the suspending means located outward from each end of the hammock, to allow the high-tension flexible suspension load bearing member to be affixed to an attachment point directly at each end, or to be attached to a carabiner at each end to connect to another extension high tension suspension load bearing member like a strap, webbing, rope or cable with an end loop to attach to each ends carabiner, and a buckle located towards the other end, to allow the extension high tension suspension load bearing member to be wrapped around an elevated vertical support point and adjusted in length to controllably shorten the extension and thereby tighten the longitudinal tension of the hammock between two elevated vertical support points.
 5. The hammock of claim 4, wherein it includes cross-braces proximal each end of the hammock, each cross brace capable of constraining the distance to the second suspension member on the opposing side of the hammock to a fixed dimension.
 6. The hammock of claim 5, wherein the cross brace has an adjustable length capable of constraining the distance to the second suspension member on the opposing side of the hammock to an adjustable dimension.
 7. The hammock of claim 6, wherein the cross brace has a hole or slot at both ends of the cross brace to allow the suspension member on one side and one end of the hammock to be routed through the hole or slot on one end of the cross-brace, and the suspension member on the opposing side and same end of the hammock to be routed through the hole or slot on the other end of the cross-brace.
 8. The hammock of claim 7 whereby tensioning the suspension members on both sides of the hammock while constrained in their lateral dimension by the cross-braces, causes the fabric support surface to drape between and below the suspension members so that an occupant may rest essentially level on the hammock bed surface in an essentially flat laying position.
 9. The hammock of claim 8, wherein both sides and both ends of the hammock have velcro, zippers, snaps or similar add-on accessory provisions attached either in discrete locations or intermittently along their lengths, or continuously along their lengths, to allow attaching accessories like netting, tenting, packing bags, cup or water bottle holders, and similar items.
 10. A kit comprising a hammock according to claim 9, and extension suspending means for attaching and suspending the hammock between upright support structures with different separation distances. 